Rotating parts of turbine engines are generally balanced with care during their construction. It happens, however, that after the assembly of the different stages, residual moments are sufficient to produce slight deformations of the shaft in rotation. These deformations generate, at high velocities, vibrations and stresses which severly affect the life of the turbine engine.
The balancing of a body in motion is ordinarly effected by the removal or addition of a certain mass of material at a predetermined distance from the axis and in a definite radial direction.
French Pat. No. 2,272,260 proposes a device to correct the imbalance of a rotor disk consisting of a certain number of weights placed at the periphery of the disk against the rim into which a plurality of grooves are machined to maintain the roots of the blades. The balancing weights are present in the form of rectangular parallelepipeds, with one of the large faces thereof carrying a plurality of tongues. The tongues are located in radial grooves provided on the lateral faces of hooks coplanar with the radial face of the rim. The weights are maintained in the radial direction between the platform of the blades and an elastic ring, the ring being placed under the weights between the hooks and the face of the disk.
This device makes it possible to obtain exact balancing both in relation to value and to direction and to remove the blades when needed without encountering particular difficulties.
This disk by disk balancing permits, however, the existence at the level of the rotor bearings a residual unbalance of slight value, which may be determined with respect to magnitude and direction, for example, by the device described in French Pat. No. 1,477,752. This device comprises a box, which contains two weights in the form of coaxial, circular sectors, angularly movable with respect to each other. The box is introduced in the hollow shaft at the bearing. With the aid of means provided to rotate the weights in relation to each other or individually, it is possible to create an additional imbalance equal to the residual imbalance and to choose the direction of the additional imbalance to exactly compensate the residual imbalance. The adjustment is effected by means of a suitable tool assembly moving in the hollow shaft and by successive testing, by starting the jet engine. In this manner, a curve is established which makes it possible to determine the value of the balancing weight and its position. With the aid of these data, the definitive balancing process is effected by a conventional method, by adding or removing material to or from the periphery of the disk.
As the compensation is made in a plane relatively far from the bearing, the results are not as good as might be expected and vibrations, while reduced, are still appreciable at the bearings.